The development and advantages of sintered, sol-gel abrasive grain, particularly sintered, sol-gel, polycrystalline, alpha alumina abrasive grain, in grinding wheels has received a large amount of attention and is well documented in the prior art literature. The use of such grain in bonded grinding wheels has been reported (U.S. Pat. No. 4,314,827 and U.S. Pat. No. 4,744,802). Sol-gel and sintering processes for alumina abrasive grit have been described in numerous patents including for example U.S. Pat. No. 4,314,827 Feb. 9, 1982 to M. A. Leitheiser et al., U.S. Pat. No. 4,623,364 Nov. 18, 1986 to T. E. Cottringer et al. and U.S. Pat. No. 4,744,802 May 17, 1988 to M. G. Schwabel. Disadvantages of fused alumina and performance advantages of sintered, sol-gel alumina abrasive grit in the grinding of metals have been taught by C. V. Rue (U.S. Pat. No. 4,543,107) and D. C. Haynes (U.S. Pat. No. 4,800,685). Haynes has also described the usefulness of a blend of fused alumina and sintered, sol-gel, alumina grains in grinding wheels. C. V. Rue has described a vitreous bonded sintered, sol-gel, alumina grain grinding wheel, wherein the grain is composed of submicron, polycrystalline, noncellular, high density alpha alumina.
Numerous variations on the sol-gel process including changes in the gel composition to include various fluxing or nucleating agents, as well variations in the conditions for carrying out the sintering process have been disclosed in the literature principally to control crystal size of the alumina. Crystal sizes of the alumina have been reported ranging from submicron (U.S. Pat. No. 4,314,827 and U.S. Pat. No. 4,623,364) to 300 microns. Despite a large amount of prior art effort on sintered, sol-gel abrasives and grinding wheels containing such abrasives there has not been the expected wide range use of such abrasives in grinding wheels, particularly vitreous bonded grinding wheels. Although C. V. Rue has reported some improvement in grinding performance with vitreous bonded sintered, sol-gel alumina grit grinding wheels, he has also noted in U.S. Pat. No. 4,543,107 some performance of such grinding wheels that is poorer than that obtained with vitreous bonded 100% fused alumina abrasive grit grinding wheels. Other disadvantages of the prior art vitreous bonded sintered, sol-gel, alumina abrasive articles, i.e. grinding wheels, have been observed during grinding of metals, including heat build up, high friction, low cutting and workpiece burn. Thus the vitreous bonded sintered, sol-gel, alumina abrasive grit grinding wheels of the art have not shown sufficient advantage, on a cost performance basis, to achieve substantial usage.
It is an object of this invention to provide an improved vitreous bonded sintered sol-gel abrasive grit abrasive article.
It is another object of this invention to provide a vitreous bonded sintered, sol-gel abrasive grit abrasive article having reduced heat build up, lower friction and improved cutting performance.
A still further object of this invention is to provide a vitreous bonded sintered, sol-gel abrasive grit abrasive article overcoming many, if not all, of the disadvantages of the prior art vitreous bonded sintered, sol-gel abrasive grit abrasive articles.